These numbers illustrate the importance of efficient techniques in managing hybrid populations, for which purpose the procedure is most widely used. Record keeping is slow, tedious, time- consuming, and expensive. Approximately 75% of the crosses made are single crosses involving only elite adapted parents. It is a modified form of pedigree method in which segregating material is handled by bulk mass method when conditions are unfavourable for selection and by pedigree method when conditions are favourable for selection. Purelines have pure adaptability due to narrow genetic base.
It favours those characteristics of plants which are related to yield and quality. Is self-fertilization an evolutionary dead end? What are demerits of pureline selection? Goulden in 1941 when he attained the F6 generation in two years by reducing the number of generations grown from a plant to one or two, while conducting multiple plantings per year, using the greenhouse and the off season. Setting new global standards for vine plant improvement. Crossing between genetically dissimilar genotypes is called hybridization. After five or six backcrosses the progeny will be hybrid for the character being transferred but like the superior parent for all other genes.
If the multiplication rate is not too variable, about 36, 50, 60 and 66 per cent of the lines are lost after 1, 2, 3 and 4 generations of bulk propagation respectively. What are cotton varieties developed by backcross technique? As the plant hormonal mechanisms are not yet understood completely, the development of in vitro cultivation and regeneration systems is still largely based on empirically testing variations of the three above mentioned factors. Because the great majority of mutants carry undesirable traits, this method has not been widely used in breeding programs. The techniques of genetic engineering, which are a part of biotechnology, will be discussed in more detail in the next chapter. The process which favours survival and further propagation of some plants having more desirable characters than others is called selection.
First, a large number of selections are made from the genetically variable original population. Selection is based not only on phenotype but also on genotype progeny row. For purposes of disease resistance, this selection can be provided by pathogens, or isolated pathotoxins that are known to have a role in pathogenesis. The aim of hybridization is to bring together desired traits found in different plant lines into one plant line via cross- pollination. This can be accomplished by first crossing a plant of the superior variety to a plant of the donor variety, which carries the trait in question, and then mating the progeny back to a plant having the genotype of the superior parent. Most of the doubled haploid populations are generated for genetic studies of various agronomic and end-use quality traits and to develop parents or cultivars resistant to Fusarium head blight. Third, polyploidy increased number of chromosome sets can contribute to crop improvement.
Marker-assisted Breeding Interest in applying molecular markers to various crop breeding endeavors has gained popularity. After hybridization, the segregating material is handled in three main ways, viz. What are main features of single seed descent method? Revisiting an old hypothesis with genetic theories and a macroevolutionary approach. Compare a pureline and a clone. Existence of self-sterility, self-incompatibility, imperfect flowers, and mechanical obstructions make the plant dependent upon foreign pollen for normal seed set.
What are main features of multilines? The strategy in plant breeding is to delay selection until at the high level of It is a procedure used primarily for breeding selfpollinated species, but can be adapted to produce inbred populations for cross-pollinated species. It favours those plant characters which are essential for survival adaptation of a species. With asexual perennials the best time is just before harvest. Comparison of mass selection and pureline selection is presented below in Table 13. It may be for different purposes like :- 1 Isolation of homozygous lines with a minimum efforts and expenses.
The chief advantage of the bulk population method is that it allows the breeder to handle very large numbers of individuals inexpensively. Such populations are characterized by a high degree of heterozygosity with tremendous free and potential genetic variation, which is maintained in a steady state by free gene flow among individuals within the populations. Main advantages of bulk breeding method are given below: i It improves adaptation of the population, because natural selection operates during bulking period. What varieties of wheat have been developed by pedigree breeding? Two types of artificial selection also are often applied: 1 destruction of plants that carry undesirable major genes and 2 mass techniques such as harvesting when only part of the seeds are mature to select for early maturing plants or the use of screens to select for increased seed size. Note that the outline if for one parental combination and that selection can be practiced in any generation! The most important methods used to achieve these goals are described below. It takes much longer time to develop a new variety. Only those breeding and selection methods are suitable for a crop which does not interfere with its natural state or ensure the maintenance of such a state.
As an example of the power of hybridization in creating variability, a cross between varieties differing by only 21 genes is capable of producing more than 10,000,000,000 different genotypes in the second generation. This method has a limited application in practical plant breeding. It is of two types, viz. What is bulk breeding method? Time of selection is a big factor, because you have to select when most of the characteristics of the plant are clearly showing. The lines are evaluated for important agronomic characteristics. In asexually propagated species, following breeding methods are used: i Plant introduction ii Clonal selection iii Heterosis breeding iv Mutation breeding v Polyploidy breeding vi Backcross method vii Distant hybridization viii Transgenic breeding ix Molecular breeding. The root growth of C22 exceeded that of C0 and the ratio of shoot dry mass to root dry mass was reduced by nearly 12%, from 8.
The parent which donates desirable character is called donor parent. What are basic requirements to start a backcross programme? At maturity the is harvested in mass, and the seeds are used to establish the next generation in a similar plot. Advantages of pureline selection are as follows: i It helps in isolating best genotypes for disease resistance, insect resistance, yield, quality- earliness etc. For teaching purpose, plant breeding is presented as four categories: Line breeding autogamous crops , population breeding crops , breeding mostly allogamous crops, some crops , clone breeding vegetatively propagated crops. Another group of selective markers are herbicide tolerance genes. Main features of a clone are given below: i The progeny of a clone is homogenous but heterozygous. Mass selection is done annually on the same plant for a minimum of three years.
Because the two genotypes were phenologically different, planting density optima are probably different for each population. Mass pedigree method was proposed by Harrington in 1937 and it was first used by him in cotton. The following breeding methods do not involve hybridization: i Plant introduction ii Pureline selection iii Mass selection iv Progeny selection v Mutation breeding vi Clonal selection vii Transgenic breeding. A foreign variety which is directly recommended for cultivation is called exotic variety. In nature as well as in genetic engineering, the agrobacteria attach to a plant cell. In genetic engineering route B, tumor inducing genes removed by other genes , transgenic cells are selected and regenerated to whole plants. Who outlined method of developing multilines? It is also known as non-recurrent parent because donor parent is used only once in the crossing programme.